I used 3 4" ports in my Build and realize now that I should have used 6" ports. When I hit higher tones, the ports vibrate (even though they are braced). 6" ports prolly wouldn't vibrate as much due to the added thickness of them and how wide they are. Hope that helps. Just get 6" ports.
Also, round ports are easy to tune if you make a mistake when building the box and cut down on port noise. Flared ports cut down on port noise that much more.
Vehicle of choice: Red 2006 Ford F-150 XL Standard Cab (ridin on black 20s)
H.U. JVC somethin
Amps: 2 Crossfire VR-1000D (2 more sitting next to me)
Electrical: Kinetik HC2000 upfront, EA 300A alt
Subs:1 RE MT 15 (1 sitting next to me)
Box:7 cube ported with 3 aeros
Speakers: Crossfire RS57 5x7 all the way round
Refs: abmw735ie32, bkolfo4, Andrizzle, Icpurplepplalot, breakjunki
Still to come: lots of 1/0 gauge, new box, batteries...
diymobileaudio.com is the DIY car audio install forum for automotive quality and spl stereo bass. 12 volt audio installation wholesalers buy amps, subs, double din car audio head unit electronics and ipod blue tooth car alarms at discounted prices